Lung cancer is a smoking-related disease and the No. 1 cancer killer in Veterans. The early detection of lung cancer by CT scan significantly reduces the mortality. CT scan is now recommended for lung cancer screening in smokers. However, CT scan dramatically increases the number of indeterminate pulmonary nodules (PNs) in asymptomatic Veterans, whereas only a small fraction of PNs are lung tumors. Given the large number of referrals to unnecessary and harmful procedures for smokers with indeterminate PNs, there is an urgent need for biomarkers that can rule out lung cancer in Veterans with PNs by specifically diagnosing the disease. We have previously developed sputum-based small non-coding RNA (ncRNA) biomarkers for diagnosis of lung cancer. However, the sensitivity and specificity of the sputum assay with only 2-3 biomarkers are not sufficient, and need to be improved by identifying and including new biomarkers. The objective of this application is to identify new lung cancer-associated small ncRNAs and develop them as sputum biomarkers that can sufficiently exclude lung cancer in Veterans with PNs. To achieve the objective, we will define a small ncRNA profile of bronchial epithelial cells of lung cancer patients, and then optimize a panel of sputum biomarkers for lung cancer using our existing sputum samples. We will also validate the performance of the new biomarker panel in newly and prospectively collected sputum specimens. The success of the project will produce a useful tool that can complement CT screening for lung cancer by ruling out lung cancer in a CT screening positive setting, and hence reduce lung cancer-related mortality in Veterans.